The effect of relative humidity on the flashover strength of solid insulation

Macpherson, R. W. and Wilson, M. P. and Timoshkin, I. V. and MacGregor, S. J. and Given, M. J.; (2020) The effect of relative humidity on the flashover strength of solid insulation. In: 2019 IEEE Pulsed Power & Plasma Science (PPPS). IEEE Pulsed Power Conference . IEEE, USA, pp. 1-4. ISBN 9781538679692 (

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This paper informs on the flashover strength of 3 materials: Delrin (Polyoxymethylene), HDPE (High Density Polyethylene) and Ultem (Polyetherimide) with 'smooth' and 'knurled' surface finishes, in zero-grade air at -0.5, 0 and 0.5 bar gauge, and at <; 10%, ~50% and >90% relative humidity (RH). All tests were completed using a 10-stage Marx generator, producing HV impulses with a nominal 100/700 ns waveshape. Each test conformed with the ASTM D3426-97 standard of 'step up' testing, to find the average flashover voltage for each set of conditions. The electrode system with each dielectric material demonstrated a decrease in breakdown voltage as the RH was increased. In high humidity environments, the knurled surface finish was seen to have a positive effect on the flashover strength of Delrin and Ultem samples, compared to a smooth, machined surface. Increasing pressure yielded an increase in the flashover strength also. For samples with a smooth surface finish, a decrease in flashover strength was found as the permittivity of the material increased, irrespective of humidity and pressure. However, a knurled surface finish had a much more erratic effect on flashover strength, with no discernible trend with increasing material permittivity